Cytokeratin 19 immunoreactivity in the diagnosis of papillary thyroid carcinoma

CONTEXT: The diagnosis of papillary thyroid carcinoma (PTC) is based on nuclear features. These features may be present in focal areas in benign thyroid diseases and follicular adenoma (FA), leading to diagnostic difficulty. AIMS: To evaluate the expression and pattern of the distribution of cytokeratin 19 (CK19) in PTC and compare its reactivity with other neoplastic and non-neoplastic conditions to assess its potential as a useful marker for PTC. MATERIALS AND METHODS: Twenty two cases of papillary carcinoma (usual type, follicular and diffuse sclerosing variant), eight follicular adenomas, eight multinodular goiters (MNG) were collected for a period of two years and six months. Sections were taken from thyroidectomy specimens fixed in 10% buffered neutral formalin. Hematoxylin and eosin staining and immunohistochemical staining for CK19 were done using standard protocol. Results were semiquantitatively scored as follows: 1+ (<5% positively stained cells), 2+ (5-25%), 3+ (25-75%) and 4+ (>75%), and then analyzed. STATISTICAL ANALYSIS AND RESULTS: All 22 (100%) papillary carcinomas showed diffuse and strong (3+ and 4+) CK19 expression. Six out of eight (75%) FAs and four out of eight (50%) MNG were positive for CK19, but it was of weaker intensity (1+ and 2+) and focal in distribution. CONCLUSION: Focal CK19 staining may be found in benign disease, but diffuse and strong positivity is characteristic of PTC, which can be used in the diagnosis of PTC in lesions of equivocal morphological appearances.